During semiconductor fabrication, currently, silicon dioxide (SiO.sub.2) obtained from the plasma reaction of TEOS with oxygen (O.sub.2), is used as the gap fill material between patterned metal lines. Unfortunately, growth of SiO.sub.2 occurs with some bread-loafing at the top of the gap which tends to cause the top of the gap opening to close before the SiO.sub.2 can completely fill the gap. Also, during normal sputter faceting, at the top edge of the gap the SiO.sub.2 becomes angled but consequently the dislodged SiO.sub.2 particles re-deposit directly below the angled edge and prematurely re-close the gap opening.
FIG. 2 depicts a typical in process wafer portion where patterned parallel lines 21 have been formed over substrate 20. An insulative layer 23 has been formed to coat patterned lines 21 and substrate 20. During deposition of layer 23 the deposited material tends to build up faster at the edges 24 of lines 21 than along the vertical walls of lines 21, thus resulting in bread-loafing. This bread-loafing at the edges 24 is problem in that any subsequent layer formed into the gaps 22 will not be able to sufficiently fill the gap before the gap opening is closed or "pinched off." Obviously, in most cases this is a highly undesirable condition as adequate isolation between lines 21 cannot be obtained.
Reliable in-situ techniques to reduce (if not eliminate) bread-loafing at the top edges of the gap opening prior to a filling the gaps with material are therefore required. The present invention provides such a technique, as will become apparent in the disclosure made hereinafter.